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Fine pitch stencils


#1

On the web site you say that the finest pitch you can handle is approximately 0.5mm. By this, do you mean that you can handle pads that are pitched at about 0.5 mm or do you mean that the smallest distance between the edges of two pads should be greater than 0.5 mm?

I am considering using an SSOP part whose legs are pitched at 0.635 mm, but the distance between the edges of pads is only 0.25 mm.

Mike


#2

Hello.

By pitch we mean the former: the distance from the center of one pad to the center of the next pad should not be less than 0.5 mm. Your SSOP part should work fine with our stencils.

- Ben


#3

I have on my board one 100-pin connector with 0.5mm pitch. The rest of the pads have a larger pitch.

I want to use a Kapton stencil for the whole board, including the 0.5mm connector, and I will reflow it. I am worried that I will have trouble reflowing the connector. I followed the manufacturer’s recommendations regarding the pcb layout and paste mask (you can see those on page 9: pewa.panasonic.com/assets/pcsd/c … atalog.pdf). However, some people experienced with reflowing these kind of connectors told me that it will be difficult to avoid bridging with this small pitch. Instead, they recommended to replace the paste mask (i.e. 100 cuts for each of the pads) with two thin lines perpendicular to the pads, one on each side of the connector. The idea is to reflow it and then rely on the surface tension to do its trick.

I am not sure what to follow. Since you have experience with this kind of connectors can you comment on this?

Thanks, Panos


#4

Hi.

Connectors like that generally are a pain (lots of hard-to-access pins, plastic might melt, leading to all kinds of issues). If you get a real, metal stencil, you should get individual apertures. I think the perpendicular bead thing is most relevant when you are manually dispensing solder paste, in which case you should definitely not mess around trying to get a dot on each pad. For a cheap stencil where you are at the limit of the process, I think it’s still preferable to go with individual apertures. After you do your print, if you get nice deposits on each pad, great; if not, you can still manually add the bead after that.

- Jan